The present invention relates to a combined white balance switching device for video and more particularly to a combined white balance switching device that improves over-all color reproduction capability by mainly employing sensor type and in case that the color temperature becomes different, switching to image signal sensing type.
As illustrated in the FIG. 1, a conventional video camera consists: a lens 1 that collects light; an image element 2 that converts light signals to electronic signals a signal processor 3 that shapes the output of the image element 2; a LPF (Low Pass Filter) 4; a mixer (Y processor and Y/C Mix) 5; a color signal shaping circuit 100 that is composed of detectors 8 at which form the color signal Gain-Controller's 9 and 10, R-Y and B-Y matrices 12 and 13, color processor 14; and a white balance circuit 200.
In the conventional video camera, the white balance circuit 200 is either of a sensor type or of an image signal sensing type.
As shown in FIG. 2, the sensor type white balance device consists of: a white balance sensor that is composed of a white cap 15, B(Blue)/R(Red) filters 16 and 17, and light receiving diodes 18 and 19; comparators 20 and 21 that compare output of the white balance sensor with a reference voltage; and controllers 22 and 23. As shown in FIG. 3, the image signal sensing white balance type device having comparators 24 and 25 that detect the image signal, compare R-Y and B-Y components of outputs with reference voltages V1 and V2, and produce adjusted voltages.
The sensor type white balance device as shown in FIG. 2 adjusts the white balance by detecting B(Blue) and R(Red) components out of incident light that come through the white cap 15 at a B(Blue) filter 16 and an R(Red) filter, comparing the B and R components with reference levels at the comparators 20 and 21, and controlling the Gain-Controller's 9 and 10 of the color signal shaping circuit 100 by control voltages b and a provided from the controllers 22 and 23. That is, when the color temperature state is "A" as shown in FIG. 4, white balance is achieved by adjusting color ratio to R:G:B1:1:1 by decreasing R-component(r) and increasing B-component(b) to match G-component(g). The image signal sensing type white balance device as shown in FIG. 3 adjusts the white balance by detecting R-Y and B-Y components from the signal line and the detected R-Y and B-Y components are compared with the reference voltages V1, V2 at the comparators 24, 25 and then control voltages c and d, which are as much as the differences between the R-Y and B-Y components, are outputted to control the Gain-Controller's 9 and 10.
In the sensor type as shown in FIG. 2, however, there is a setback that correct color reproduction cannot be achieved when there is a difference between a color temperature sensed by the sensor and a color temperature of a spot to which incident light through the lens is cast, because the white balance is performed by using the sensor in disregard of the image signal. On the other hand, in the image signal sensing type as shown in FIG. 3, the setback of the sensor type does not exist but there are other setbacks: one that single color having particularly R,G, or B component is recognized as the white color during processing images, so that color adjustment is performed based on that recognition; another that color is hampered when zooming is performed.